Examples of valve operating systems that incorporate a summation mechanism are shown in the Applicants' earlier EP 1417399, EP 2142768, EP 2257697 and EP 2242912 which are imported herein by reference. Cam summation mechanisms need to have a clearance between at least one of the cam followers and its associated cam at some points in the camshaft rotation cycle, and it is known to provide a control spring to hold the summation lever in contact with one of the cam profiles so that its position is fully defined when there is clearance in the system. The amount of clearance needs to be adjusted in order to ensure that the valve lift is well matched between the different cylinders of the engine and to eliminate manufacturing tolerance variations in the various valvetrain components of the system, and variations in the cylinder head machining.
Conventional valvetrain systems also need to compensate for manufacturing variations and in many cases this is achieved by using a hydraulic lash adjuster that increases in length until the cam follower is held in contact with the cam lobe. Hydraulic lash adjusters have the advantages of allowing the system to compensate for temperature changes while the engine is running, compensating for any wear that occurs over the life of the engine, and eliminating the need for any manual adjustment of the system at the time of assembly.
A cam summation system using a hydraulic lash adjuster requires some form of stop in order to limit the expansion of the lash adjuster and to maintain the correct amount of clearance. In the absence of such a stop, the lash adjuster would continue to inflate until it has removed all of the clearance from the system. EP 1417399 shows a variety of different methods for maintaining and adjusting the amount of clearance in the system when a hydraulic lash adjuster is used.
FIGS. 5 and 6 of the latter patent show that the clearance can be controlled by setting the distance between the centre of the camshaft and the centre of the pivot shaft connecting the summation lever to the valve actuating rockers. Setting the distance between the centre of the camshaft and the centre of the pivot shaft is a particularly advantageous way of controlling the clearance because it still allows the hydraulic lash adjuster to compensate for the effects of thermal expansion in the cylinder head and to compensate for any variation in valve tip position due to tolerances, or due to wear over the life of the engine. Consequently, it is possible to adjust the clearance of the system as soon as a particular cam summation mechanism becomes associated with a particular group of cam lobes, and this adjustment can be completed before the system is fitted to the cylinder head.
Alternative designs to those disclosed in EP 1417399 have been proposed in order to achieve the same result by providing a cylindrical contact surface on the camshaft that contacts a corresponding surface either on the summation lever or on the valve actuating rocker(s).
A still further earlier proposal has been to rely on an eccentric pivot shaft or an eccentric cam follower axle as disclosed in FIGS. 4D and 5B of EP 2257697.
The method by which the clearance adjustment is achieved is not important to the present invention, which can be applied with any of the alternative designs discussed above.
The task of assembling of a complete valve operating system that incorporates a camshaft and one or more cam summation mechanisms is complicated because it is necessary to align each of several independently movable cam actuating rockers with a valve stem at one end and a pivot element, such as a lash adjuster, at the other as the camshaft is lowered into position. Furthermore, it is necessary to secure in position the control springs connected to the cam summation levers to urge the cam followers against their respective cam surfaces.